X-Ray Luminescence of ZnO Tetrapods Grown in the Presence of Copper and Gold Admixtures in Initial Charge

Optics and Spectroscopy - We investigated the morphology and luminescent properties of ZnO tetrapod powders with copper and gold admixtures, obtained by carbothermal pyrolysis. A broad band in the...     

The kinetics of formation of aerosols in gas flows

It was shown for the example of CsI aerosol that the aggregation of primary aerosol particles could be described in terms of either the discrete or continuum model. This conclusion was drawn on the basis of experiments performed by the method that allowed primary particles to be observed against the background of their aggregates and transfer of primary particles from aerosol volume to a collector to be provided. The size of primary particles on the collector was determined by transmission electron microscopy. It was found that, under the conditions used, the size distribution of primary particles corresponded to the Fokker-Planck equation.     

Method of analysis of mathematical models of media under complex loading

A method of analysis of constitutive models of media with complex loading trajectories is proposed. It is based on a comparison of data from laboratory experiments and corresponding results of numerical calculations. In previous laboratory experiments, nearly homogeneous complex loading with continuous rotation of the principal axes of the strain tensor and loading with broken strain trajectories was performed. Numerical calculations for the types of loading corresponding to the experiments performed are based on the constitutive equations of the model. The numerical results obtained and data of the laboratory experiments are compared. The hypoplastic model of a geomedium is analyzed. Analysis shows that the model is a satisfactory qualitative and quantitative approximation of data from laboratory experiments on complex loading of geomaterials. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 5, pp. 133–142, September–October, 1999.     

Electrization of nanocrystals in flows of supersaturated vapors

It is found that nano- and microcrystals of a number of compounds grown in ion-free vapor of high supersaturation acquire electric charge. The electrophoretic mobility of these crystals changes, as is demonstrated by the data concerning aerosols formed in cooling the vapor above boiling melts of a number of substances (boiling temperature, 500?C1800 K) placed into a 300 K carrier gas. Nano- and microparticles assembled into aggregates are found in flows of the cooled vapor. It is found that the application of an electric field with an intensity of 150?C1000 V/cm induces the movement of particles toward the negatively charged electrode at a rate of 5?C15 cm/s, the speed of their movement being related linearly to the field intensity and corresponding to the presence of ??10³ charge carriers per every particle. It is established that the experimental data are in accordance with the assumption that the growth of each particle results in the decomposition of vapor molecules adsorbed by the particle into ions with the nonequivalent liberation of cations and anions into vapor; i.e., an adsorption-ionization-desorption route for the charging of growing particles is discovered.     

Nanocrystalline zinc oxide: Pyrolytic synthesis and spectroscopic characteristics

Nanocrystalline and microcrystalline ZnO powders are synthesized by the pyrolysis of organic zinc salts in the presence of a reducing catalyst represented by a porous cellulose carrier. The specimens obtained are characterized by X-ray powder diffraction, energy dispersive analysis, scanning electron microscopy, and pulse cathodoluminescence. Lasing characteristics of the specimens are studied. The synthesis conditions, under which specimens with the crystallite morphology optimal for a low-threshold lasing are obtained, are found.     

Calculation of the Differential Rotation of a Rigid Core in Hypoplastic Media under Complex Loading

The plane problem of calculating the directional transfer of internal masses and the differential rotation of an internal rigid core is considered for hypoplastic media with continuous rotation of the principal axes of the strain tensor under complex loading. The hypoplastic model of granular media with internal variables is used as the basic model. A numerical algorithm for calculating stress and velocity fields in an inelastic medium under complex loading is developed using the finiteelement method. Mechanical trajectories of material points of the medium are calculated and the rotational velocity of the core and the reduction coefficient are estimated.     

Analysis of Laser Action in ZnO Tetrapods Obtained by Carbothermal Synthesis

JETP Letters - Lasing in ZnO tetrapods produced by pyrolytic carbothermal synthesis is investigated. Since a tetrapod can have several optical cavities, which complicates analysis, emission from...     

High-temperature lasing in ZnO microcrystallites

High-temperature studies of the luminescence and lasing spectra parameters of the main UV bands (spontaneous luminescence and lines of stimulated-emission mode structure) and the recombination band of electron-hole plasma in zinc oxide microcrystallites have been performed. ZnO microcrystallites of tetrapod morphology, characterized by type-II lasing (microlasers), have been chosen as objects of study [1]. The temperature behavior of a number of key parameters related to specific features of microlasing is investigated.